The present invention is directed to parts used in an outdoor or other corrosive environment and, more particularly, to an aluminum alloy part used in a corrosive environment.
Many parts used in an outdoor or other corrosive environment are manufactured from aluminum alloys. Such parts often are used in airplanes, automobiles, bicycles and fishing equipment. While aluminum alloys achieve strengths comparatively higher than steel through the use of a heat treatment, aluminum alloys also have relatively inferior corrosion resistance. Consequently, a surface treatment known as an alumite process normally is applied to aluminum alloy parts as a means to improve corrosion resistance.
Unfortunately, the alumite process itself creates some problems as shown in FIGS. 1(A)-1(C). As shown in FIG. 1(A), metallic compounds 215 (e.g., CuAl2, copper or zinc) may exist within portions of a part main body 210 of an aluminum alloy part 200. When the alumite process is applied to the part main body 210 of aluminum alloy part 200 to form an alumite coating 221, the metallic compounds 215 may undergo priority fusing, thus creating a coating flaw 222 in the form of a void or recess as shown in FIG. 1(B). As a result, the alumite coating 221 does not adequately cover all of the aluminum alloy part 200. Then, when aluminum alloy part 200 is subjected to the corrosive environment, corrosion expands coating flaw 222 as shown in FIG. 1(C). Sometimes a sealing process is applied to reduce corrosion of coating flaw 222, but such sealing processes tend to inadequately control the spread of corrosion.
Japanese Laid-Open Patent Publication No. 1994-192888 discloses a method intended to improve the corrosion resistance of an aluminum alloy part by increasing the thickness of an alumite layer and by electrodepositing a cation resin onto the aluminum alloy part after the alumite process. While increasing the thickness of the alumite layer may improve corrosion resistance, it becomes more difficult to maintain a high-quality metallic luster of the aluminum alloy part. On the other hand, if the alumite process is not applied to the aluminum alloy part, then good corrosion resistance of the aluminum alloy part is lost.